Lithographic offset printing utilizes printing plates having a non-image area and an image area. With proper treatment, the image areas are hydrophobic and receptive to inks, and the non-image areas are hydrophilic and water receptive. During the printing process, it is necessary to continuously treat the plate with a water-based fountain solution (dampening solution) in order to maintain the hydrophilic character on the non-image areas.
While an offset printing press is running, fountain solution is continuously applied to the printing plate just before the application of the printing ink. The fountain solution is formulated to have an affinity for the non-image, hydrophilic areas of the plate and wets these areas. The thin film of fountain solution prevents the subsequent application of ink from covering the plate in a non-image area.
Fountain solution compositions vary widely to meet an assortment of applications. Different plate materials such as paper, polyester, and anodized aluminum require different chemistries. The type of printing, ink, paper, water and dampening system also plays a role in the type of fountain solution to be used.
A fountain solution or press ready mix is generally made from a fountain solution concentrate and water for most web applications, plus alcohol or an alcohol substitute for sheet fed and certain web applications. A fountain solution concentrate typically includes about 50-80% by wt water and selected components including film-formers such as gums, synthetic polymers, complex sugars, surfactants, solvents, acids and buffering agents to maintain the pH, desensitizing agents, biocides, non-piling agents, and chelating agents for hard water salts, for example. The surfactants and alcohol or alcohol substitutes act to promote plate wetting by lowering the surface tension of water to make the fountain solution spread more efficiently across the plate surface. The combination of components provide an environment that keeps the plate printing clean while maintaining good ink and water balance. Typically, a standard fountain concentrate is diluted with water to an about 1-5% by volume concentration in a day tank or recirculating system, more commonly to an about 3-5% by volume concentration.
Depicted in FIG. 1, is an exemplary conventional prior art system 10 for preparing fountain solutions that includes a mixing apparatus 12. In conventional systems, a pre-mixed fountain solution concentrate 14 and a water source 16 are flowed through inlets 18a, 18b into a mixer 12, and the reconstituted fountain solution 20 is flowed out of the mixer through a product outlet 22 to a supply tank (day tank) 24. The fountain solution 20 is conveyed through conduit 25 to a recirculating tank 26 where it is chilled to about 45-60° F., and then conveyed through conduit 27a to a press unit 28 for application to a printing plate (not shown). The used fountain solution 20 is then returned through conduit 27b to the recirculating tank 26 for re-cooling.
Thus, with conventional systems, a single concentrate containing the chemical components of a fountain solution is prepared ex situ and then diluted with water to provide a press-ready composition. In cases where an increase in desensitizer is required for a given plate type, the concentration of the fountain solution concentrate is increased, which also increases the concentration of wetting agents and other components of the fountain solution. In certain situations, the increased concentration of such other components can disturb the ink and water balance and reduce the quality of the printed image. It would be desirable to provide a system and a process that eliminates such disadvantages. It would also be desirable to provide a system that eliminates water from the fountain solution concentrate to conserve on space, usage rates and shipping costs.